The present invention relates generally to a metal line of a semiconductor device and a method for forming the same, and more particularly, to a metal line of a semiconductor device that can improve the characteristics of a diffusion barrier and can thereby improve the characteristics and the reliability of a semiconductor device and a method for forming the same.
In a semiconductor device, metal lines are formed to electrically connect elements or lines with each other. Contact plugs are formed to connect lower metal lines and upper metal lines with each other. As the integration level of the semiconductor device continues to increase, the aspect ratio of a contact hole, in which a contact plug is formed, gradually increases. As a result, the difficulty and the importance of a process for forming the metal line and the contact plug have been noted.
The metal line of a semiconductor device is usually formed of aluminum or tungsten because both have good electrical conductivity. Copper is being studied as a potential next-generation material for a metal line because copper has excellent electrical conductivity and low resistance when compared to aluminum and tungsten. Forming the metal line of a semiconductor device with copper (Cu) can therefore solve the problems associated with conventional metal lines of highly integrated semiconductor devices having high operating speed such as RC signal delay.
It is difficult to dry etch copper into a wiring pattern, and therefore, to form a metal line using copper, a damascene process is employed. In the damascene metal line forming process, a damascene pattern is formed by etching an interlayer dielectric, and a metal line is formed by filling a copper layer in the damascene pattern. The damascene process can be a single damascene process or a dual damascene process.
When applying the damascene process, in a multi-layered metal line, an upper metal line and a contact plug for connecting the upper metal line and a lower metal line can be simultaneously formed. Also, since surface undulations that are produced due to the presence of the metal line can be removed, a subsequent process can be conveniently conducted.
Further, in the case of using copper as the material for the metal line, as opposed to the case of using aluminum, copper diffuses to a semiconductor substrate through the interlayer dielectric. The diffused copper acts as deep-level impurities in the semiconductor substrate made of silicon and induces leakage current. Therefore, it is necessary to form a diffusion barrier at an interface between a copper layer and the interlayer dielectric. Generally, the diffusion barrier is made of a Ta layer or a TaN layer.
However, in the conventional art as described above, when manufacturing a highly integrated semiconductor device, the characteristics of the diffusion barrier made of the Ta layer or the TaN layer are likely to deteriorate, and leakage current is likely to be induced, and as a result, the characteristics and the reliability of the semiconductor device are degraded. Thickness of the diffusion barrier may be increased to improve the characteristics of the diffusion barrier, however, when the diffusion barrier thickness is increased the contact resistance increases as well. This increase in the contact resistance is not desirable.